The present invention relates to a method of driving a liquid crystal display (LCD), especially a simple matrix type LCD, a drive IC for the method and a drive circuit using the drive IC.
An LCD has been widely used in a personal computer, a word processor, and other electronic equipment for its thin and light features, while its display capacity has been increased rapidly. Especially, a super twisted nematic (STN) type LCD is widely used in inexpensive equipment since its cost is lower than a thin film transistor (TFT) type LCD.
An STN type LCD increases its display capacity by increasing a twist angle of a liquid crystal molecule more than two hundred degrees so as to sharpen electro-optical properties of a threshold characteristic of the LCD. The STN type LCD can be manufactured at a low cost compared to a TFT type LCD that has an active matrix structure with a switching element for each pixel.
A multiplex drive method is generally used for driving a simple matrix type LCD including the STN type LCD. The simple matrix LCD has no switching element for each pixel, so that a display intensity of a pixel depends on a root mean square (rms) value voltage including a state in which the scanning electrode of the pixel is not selected. This multiplex drive method keeps display uniformity by making rms voltages equal between enabled pixels as well as disabled pixels.
FIG. 47 shows the above mentioned drive method. Numeral 503 is an LCD panel, 504-507 are scanning electrodes, and 508-511 are signal electrodes. A scanning voltage pulse (+Vs) 501 is applied to the scanning electrodes in order, and signal voltage 502 is applied to the signal electrode, where the signal voltage 502 corresponds to on/off states of the pixel on the selected scanning electrode. The signal voltage is xe2x88x92Vd for the on state and +Vd for the off state. The polarity of the voltage is reversed over a predetermined period to apply an alternating voltage to the liquid crystal.
In a real LCD panel, there is a switching distortion of the voltage wave form applied to the liquid crystal, due to a CR circuit made of an electrode resistance of the scanning electrode and/or the signal electrode, an output resistance of the drive IC and a capacitance of the liquid crystal. Therefore, the rms voltage applied to each pixel deviates from an ideal value, so that the intensity of the pixel, which should be constant, varies depending on a display pattern of other parts. This phenomenon is xe2x80x9cso-called crosstalkxe2x80x9d.
There are several causes of such a crosstalk. The most important and basic cause is a switching distortion of a data signal. In FIG. 47, though only four scanning electrodes 504-507 are shown, there are plural electrodes following the electrode 507, and all pixels are supposed to be in the on state (i.e., white is displayed). For example, the signal voltage applied to the signal electrode 509 is switched three times between off and on states during scanning periods of the scanning electrodes 504-507, while the signal voltage applied to the signal electrode 508 maintains the on state without switching. Therefore, pixels on the signal electrode 509 are provided with a lower rms voltage due to the switching distortion compared with the pixels on the signal electrodes 508. As a result, the white level of the pixels on the signal electrode 509 is darker than that of the pixels on the signal electrode 508, so that stripes are displayed even though the display data are all white. This crosstalk is called a character crosstalk.
In a liquid crystal display, a dc voltage is prevented from being applied to the liquid crystal by switching the polarity of the scanning voltage as well as the polarity of the signal voltage of the data signal in a predetermined period. A drive method for decreasing the character crosstalk is disclosed in Japanese laid open patent application (Tokukai-Sho) 60-19195 and the technical report of Japanese Television Gakkai, IPD82-4 (1983). In this drive method, the switching frequency of the driving voltage polarity is increased in a constant intensity display part by switching drive voltage polarity based on a period of plural horizontal scanning periods that is shorter than one frame. Currently, it is normal to switch the polarity every 10-30 horizontal scanning periods, that is one to several tens of switching frequency per one frame in an LCD having 200-500 scanning lines.
However, this drive method can not eliminate the character crosstalk completely. In addition, this drive method may create another crosstalk (vertical line crosstalk) when a vertical bar is displayed since the polarity switching generates a voltage distortion on the scanning electrode (refer the text of The Second Fine Process Technology Japan 92 Seminar R17).
Another drive method is explained in Japanese laid open patent application (Tokukai-Hei) 4-360192 or 8-292744. This method suppresses the crosstalk by shifting the output level of the signal voltage so as to compensate the switching distortion when the signal voltage switches its level with regard to the non-selected level of the scanning voltage. As shown in FIG. 48, when the output level of the signal voltage is switched, a compensating pulse 521 is added, which shifts the output level of the signal voltage for a predetermined period, so as to compensate for an rms voltage decrease due to the waveform distortion. In this Figure, the non-selected level of the scanning voltage is shifted from V1 to V 4 when the polarity of the scanning voltage is switched, for controlling the output voltage of a scanning IC.
FIG. 49 shows a drive circuit for obtaining the wave form shown in FIG. 48 as disclosed in Tokukai-Hei 4-360192. This drive circuit generates four additional voltage levels VDD, V2, V3, V5. An LCD driving voltage generator 525 generates ten voltage levels VDD, VDxe2x80x2, V1-V5, V2xe2x80x2, V3xe2x80x2 and V5xe2x80x2, and eight levels of them are supplied to a signal drive circuit 523. Numeral 522 is an LCD panel and 524 is a scan drive circuit.
If the non-selected level of the scanning voltage is a constant value V1, the signal voltage waveform is as shown in FIG. 50. This is obtained by shifting the latter half of the signal voltage waveform in FIG. 48. The scanning IC is required to output positive and negative pulses (+/xe2x88x92Vs), and the lower half of the voltage level generated by the LCD scan voltage generator 525 is not necessary.
In the drive method disclosed in Tokukai-Hei 8-292744, a compensating pulse is superimposed on the supplied voltage to the signal drive circuit for obtaining the waveform shown in FIG. 48 or FIG. 50. This drive method makes the output of the signal drive IC high impedance so that the compensating pulse does not reach the signal electrode when the signal voltage is not switched (is not inverted), and turn on the output of the signal drive IC so that the compensating pulse is applied to the signal electrode when the signal voltage is switched (is inverted).
Another drive method is disclosed in Tokukai-Hei 5-33331. This drive method adds a pulse voltage that decreases the rms signal voltage when the signal voltage is not inverted, opposite to the above mentioned method disclosed in Tokukai-Hei 4-360192 or 8-292744, so as to generate a waveform distortion that may occur when the level is inverted and makes both rms voltages equal. The non-selected level of the scanning electrode or the opposite level of the signal voltage (the off level when continuing on signal, and the on level when continuing off signal) is used as a compensation voltage level, so that the crosstalk is suppressed without additional voltage levels.
The above mentioned drive methods in the prior art have some disadvantages as explained below.
In the method of Tokukai-Hei 4-360192, the number of the voltage levels supplied to the LCD drive IC is increased, along with the numbers of bus wires and switches in the drive IC as well as the numbers of connections between the drive IC and a power source circuit. The number of the voltage levels supplied to the signal drive IC is increased from four to eight when using the waveform of FIG. 48, and from two to four when using the waveform of FIG. 50, by adding the compensating pulse. Thus, areas of the drive IC and the connecting portion are increased, so that the cost of the IC rises and the area of a peripheral portion of the LCD panel increases.
In the drive method disclosed in Tokukai-Hei 8-292744, while the output of the signal drive IC is in a high impedance state, the signal electrode corresponding to the output is in a floating state, so that the signal electrode discharges. As a result, contrast of the LCD drops, and an uneven display state may occur.
In the drive method disclosed in Tokukai-Hei 5-333315, the level of the compensation voltage is shared with another voltage level, so that the voltage switching width for the compensation is large. In this method, a large voltage switching occurred once during one horizontal scan period when the signal voltage is inverted, and twice for leading and falling edges of the compensating pulse during one horizontal scan period when the signal voltage is not inverted. On the other hand, the drive method without compensation of the crosstalk does not caiuse the voltage switching when the signal voltage is not inverted. When the number of scan lines is n, the signal voltage switchings occur nxe2x88x922n times in the drive method disclosed in Tokukai-Hei 5-333315. This number nxe2x88x922n is much bigger than 0xe2x88x92n that is the number of switching in the drive method without compensation of the crosstalk. The consumption of power also increases along with the number of switchings.
Furthermore, in any drive method mentioned above, the compensation waveform has high frequency components, so that the compensation is not even in the screen, and compensation characteristics may vary depending on a size of the LCD panel, a number of pixels and physical constants of the liquid crystal.
The main purpose of the present invention is to improve the above mentioned drive method in the prior art so that the crosstalk is eliminated or decreased and to suppress increasing of the area of the peripheral portion of an LCD as well as a cost and a power consumption of a drive IC, thus realizing an inexpensive and low-power LCD.
A first drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; adding a compensating pulse to the signal voltage of the signal electrode that changes from a negative level to a positive level for two consecutive horizontal scanning periods during a first predetermined period so as to compensate a drop of a rms voltage due to a waveform distortion accompanying the level change of the signal voltage; and adding a compensating pulse to the signal voltage of the signal electrode that changes from a positive level to a negative level between two consecutive horizontal scanning periods during a second predetermined period so as to compensate a drop of a rms voltage due to a waveform distortion accompanying the level change of the signal voltage.
A second drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; adding a compensating pulse to the signal voltage of the signal electrode that maintains a positive level for two consecutive horizontal scanning periods during a first predetermined period so as to give a drop of a rms voltage that would be generated if the level of the signal voltage changes its level and generates a waveform distortion; and adding a compensating pulse to the signal voltage of the signal electrode that maintains a negative level for two consecutive horizontal scanning periods during a second predetermined period so as to give a drop of a rms voltage that would be generated if the level of the signal voltage changes its level and generate a waveform distortion.
According to the above mentioned first or second method, variability of the rms signal voltage is suppressed by the compensating pulse, so that the crosstalk is reduced. In addition, since signal electrodes, to which the compensating pulse is added, are restricted as mentioned above, the number of required voltage levels is decreased compared with the case where there is not such a restriction. Therefore, a number of switches and wires in a drive IC is reduced, the area of a drive IC is reduced, a peripheral portion of the display becomes compact, and the drive IC becomes inexpensive. In addition, power consumption does not increase, and the display unevenness due to a power source noise hardly appears.
In the first and second drive method, it is preferable that the first and second predetermined periods are substantially equal for preventing a dc voltage from being applied to the liquid crystal when adding the compensating pulse. If the dc voltage is applied, the properties of the liquid crystal may deteriorate.
It is also preferable in the first and second drive method that the first and second predetermined periods are set in accordance with a polarity signal (signal for inverting the polarity), so that the first and second predetermined periods can be adjusted without using a special control signal. In this case, it is preferable to determine wheather or not to add the compensation pulse in accordance with a logic condition using the display data for simplifying the logic table or circuit.
Alternatively, the first and second predetermined periods can be set using not only the polarity signal but also another control signal. For example, the relation between the two predetermined periods and the polarity signal may be inverted with every period of the control signal that is longer than the polarity changing period. In this case too, it is preferable to determine wherather or not to add the compensation pulse in accordance with a logic condition using the display data.
Alternatively, the first and second predetermined periods can be set using only another control signal set independently from the polarity signal.
A third drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode that changes its level for two consecutive horizontal scanning periods so as to compensate a drop of a rms voltage due to a waveform distortion accompanying the level change of the signal voltage, in such a way that the positive and negative compensating pulses do not overlap in a horizontal scanning period.
A fourth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrode; and adding a compensating pulse to the signal voltage of the signal electrode that maintains the same level for two consecutive horizontal scanning periods so as to give a drop of a rms voltage that would be generated if the level of the signal voltage changes its level and generates a waveform distortion, in such a way that the compensating pulses, which are added to the signal electrodes whose signal voltage maintains a positive or negative level, do not overlap in a horizontal scanning period.
According to the third or fourth drive method, the variability of the rms signal voltage is suppressed by the compensating pulse, so that the character crosstalk is eliminated or reduced. Moreover, the signal electrodes to which the compensating pulse is added are restricted as mentioned above, so that the required voltage levels are not many. As a result, the area of the drive IC can be reduced, the peripheral area of the LCD can be compact, and the drive IC can be inexpensive. In addition, compared with the first or second drive method, the third drive method disposes the positive and negative compensating pulses closely to each other, so that the dc voltage and low frequency components of the pixel voltage are reduced and a flicker is hardly generated.
It is preferable in the third or fourth drive method to add a first kind of compensating pulse in a first period of the horizontal scanning period, and to add a second kind of compensating pulse in a second period. Thus, a circuit for obtaining the waveforms mentioned above can be easily made.
A fifth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes via a first electric path; and adding a compensating pulse to the signal voltage via a second electric path whose impedance is higher than that of the first electric path, so as to compensate a drop of a rms voltage due to a waveform distortion accompanying the level change of the signal voltage. This drive method can be combined with the first through fourth drive methods.
Thus, the area of the drive IC can be reduced since the impedance of the second electric path for the compensating pulse (the signal voltage with the compensating pulse), i.e., an output resistance or bus resistance, can be higher than the first electric path for the normal signals. As a result, peripherals of the LCD can be compact, and the drive IC can be inexpensive. A power source for the compensating pulse can be inexpensive and easy to design since a power source with low current capacity can be used.
A sixth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode that changes its level for two consecutive horizontal scanning periods so as to compensate a drop of a rms voltage due to a waveform distortion accompanying the level change of the signal voltage, wherein a width of the compensating pulse is more than one and one half of the time constant Bin of a pixel, which is given by the following equation,
Bin=(Rpixxc3x97n)xc3x97(Cpixxc3x97n)/2,
where Rpix is a resistance of the signal electrode per one pixel, Cpix is a capacitance per one pixel, and n is a number of pixels per one signal line.
A seventh drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode that maintains the same level for two consecutive horizontal scanning periods so as to give a drop of a rms voltage that would be generated if the level of the signal voltage changes its level and generates a waveform distortion, wherein a width of the compensating pulse is more than one and one half of the time constant Bin of a pixel, which is given by the above mentioned equation in the sixth drive method.
According to the sixth or seventh drive method of the present invention, a voltage difference of the compensating pulse in the LCD panel due to the decrease or distortion of the compensating pulse can be suppressed, so that a uniform display in the LCD panel can be obtained. It is more preferable that the width of the compensating pulse is more than four times of the time constant Bin in the sixth and seventh drive method.
An eighth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode that changes its level for two consecutive horizontal scanning periods so as to compensate a drop of a rms voltage due to a waveform distortion accompanying the level change of the signal voltage, wherein the compensation pulse has a shape whose frequency component is lower than that of a rectangular wave.
A ninth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode that maintains a same level for two consecutive horizontal scanning periods so as to give a drop of a rms voltage that would be generated if the level of the signal voltage changes its level and generates a waveform distortion, wherein the compensation pulse has a shape whose frequency component is lower than that of a rectangular wave.
According to the eighth or ninth drive method of the present invention, a voltage variability of the compensating pulse in the LCD panel due to the decrease or distortion of the compensating pulse can be suppressed, so that a more uniform display in the LCD panel can be obtained compared with the sixth or seventh drive method. For example, a sine wave, a triangle wave or an arc wave can be used as well as a rectangular wave for the compensating pulse. The rectangular wave can simplify the power source circuits. On the other hands, the sine wave can provide an effective compensation since the sine wave includes low frequency components and is hardly distorted or decreased.
A tenth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode in accordance with a level change of the signal voltage for two consecutive horizontal scanning periods, wherein the signal voltage has gentle rising and falling edges. According to this drive method, the distortion of the signal voltage is small and a small compensation amount is enough to compensate a small crosstalk. In addition, uniformity of a display can be obtained easily.
An eleventh drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode in accordance with a level change of the signal voltage for two consecutive horizontal scanning periods, wherein add timing and a pulse width of the compensating pulse are controlled by a compensating pulse control signal set according to a count value of a clock. According to this drive method, the rms voltage of the compensating pulse can be adjusted easily according to the properties of the LCD panel.
A twelfth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode in accordance with a level change of the signal voltage for two consecutive horizontal scanning periods, wherein at least one of the height and width of the compensating pulse varies gradually from the point nearest to a power source to the point farthest from a power source. The amount of the crosstalk due to the waveform distortion usually varies in accordance with the distance from the scan drive circuit. According to the twelfth drive method of the present invention, uniformity of display can be maintained in spite of the above mentioned phenomenon since the width and/or height (i.e., the compensation amount) is varied in accordance with the amount of the crosstalk.
A thirteenth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode in accordance with a level change of the signal voltage for two consecutive horizontal scanning periods, wherein at least one of the height and width of the compensating pulse is controlled in accordance with a difference of numbers of on-pixels or off-pixels between two scanning electrodes corresponding to the two consecutive horizontal scanning periods. According to this drive method, the compensation amount can be adjusted in accordance with a crosstalk amount due to a voltage distortion on the scanning electrode from a specific a display pattern, so that the uniformity of a display is improved.
A fourteenth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; applying a signal voltage to the plural signal electrodes; and adding a compensating pulse to the signal voltage of the signal electrode in accordance with a level change of the signal voltage for two consecutive horizontal scanning periods, wherein the compensating pulse added in the upper part and the compensating pulse added in the lower part are controlled independently from each other. According to this drive method, the compensation amount can be controlled in accordance with a crosstalk amount that may be different between upper and lower parts of the display depending on the specific display pattern. Thus the crosstalk compensation can be performed properly both in the upper and lower parts of the display, and a boundary line between the upper and lower parts of the display can be suppressed.
A fifteenth drive method according to the present invention comprises the steps of applying a scanning voltage to the plural scanning electrodes in order; and applying a signal voltage to the plural signal electrodes, wherein the signal voltage includes positive and negative halves of a sine wave voltage. According to this drive method, the rising and falling edges of the signal voltage become gentle so that the waveform distortion is hardly generated. In addition, when the polarity does not change, the rms voltage drop is generated in the same way as when the polarity changes since the voltage drops once and returns to the original level.
In the above mentioned drive method, it is preferable to cut at least one of the positive and negative compensating pulses partially by a phase control. Thus, the compensation amount is adjusted between the positive and negative compensating pulses to obtain good display properties.
According to each drive method mentioned above, the polarity of the scanning voltage is not required to change so often. It is preferable that the change period of the scanning voltage polarity is longer than one fourth of the frame period. In other words, it is preferable to change the polarity of the scanning voltage less than four times per one frame. There is no problem if the polarity of the scanning voltage is changed only once per one frame. Thus, the vertical line crosstalk due to the distortion of the scanning voltage can be reduced.
A first configuration of the drive IC for an LCD according to the present invention that is suitable for the above mentioned drive methods comprises a first latch circuit for keeping first signal data in a first horizontal scanning period; a second latch circuit for keeping second signal data in a second horizontal scanning period; a set of switch circuits for selecting one of plural input voltages and supplying the selected voltage in accordance with output signals of the first and second latches; and a plurality of bus lines, at least one of which is used by plural voltage levels (preferably voltage levels of the compensating pulse). According to this configuration, the numbers of bus lines and output switches are reduced, so that the area of the drive IC can be reduced, the peripheral portion of the LCD panel can be compacted and the drive IC can be reduced in cost.
A second configuration of the drive IC for an LCD according to the present invention comprises a first latch circuit for keeping first signal data in a first horizontal scanning period; a second latch circuit for keeping second signal data in a second horizontal scanning period; a set of switch circuits for selecting one of plural input voltages and supplying the selected voltage in accordance with output signals of the first and second latches; a plurality of bus lines; and an inverter circuit for inverting at least one of the voltage levels (preferably a voltage level of the compensating pulse) on the plural bus lines in accordance with a control signal. According to this configuration, the numbers of bus lines and output switches are reduced, so that the area of the drive IC can be reduced, the peripheral portion of the LCD panel can be compacted and the drive IC can be reduced in cost.
A third configuration of the drive IC for an LCD according to the present invention comprises a first latch circuit for keeping first signal data in a first horizontal scanning period; a second latch circuit for keeping second signal data in a second horizontal scanning period adjacent to the first horizontal scanning period; and a set of switch circuits for selecting one of plural input voltages and supplying the selected voltage in accordance with output signals of the first and second latches, wherein at least one of the switch circuits has a larger output resistance than other switch circuits.
It is preferable that the switch circuit for selecting the voltage level of the compensating pulse has a larger output resistance than other switch circuits. Moreover, it is preferable that the switch circuit connected to the bus line that is used by plural voltage levels has a larger output resistance than other switch circuits. Alternatively, it is preferable that the switch circuit connected to the bus line whose voltage level is inverted has a larger output resistance than other switch circuits. In addition, the switch circuit has an output resistance preferably within 2-50 times and more preferably within 5-20 times of the resistance of other switch circuits.
Thus, the area of the drive IC can be reduced for compacting the peripheral circuit of the LCD panel and reducing the cost of the drive IC.
A fourth configuration of the drive IC for an LCD according to the present invention comprises a first latch circuit for keeping first signal data in a first horizontal scanning period; a second latch circuit for keeping second signal data in a second horizontal scanning period adjacent to the first horizontal scanning period; a set of switch circuits for selecting one of plural input voltages and supplying the selected voltage in accordance with output signals of the first and second latches; and a plurality of bus lines, wherein at least one of the bus lines (preferably the bus line to which the voltage level of the compensating pulse is supplied) has a larger resistance than other bus lines. According to this configuration, the width of the bus line can be narrow so that the area of the drive IC can be reduced for compacting the peripheral circuit of LCD panel and reducing the cost of the drive IC.
A fifth configuration of the drive IC for an LCD according to the present invention comprises a first latch circuit for keeping first signal data in a first horizontal scanning period; a second latch circuit for keeping second signal data in a second horizontal scanning period adjacent to the first horizontal scanning period; a set of switch circuits for selecting one of plural input voltages and supplying the selected voltage in accordance with output signals of the first and second latches; a plurality of bus lines, with the switch circuits selecting one of three voltages including a compensating voltage having a varying level. By this configuration too, the area of the drive IC can be reduced for compacting the peripheral circuit of LCD panel and reducing the cost of the drive IC.
A first configuration of the drive circuit for an LCD according to the present invention comprises a signal drive circuit using the above explained drive IC and a power source circuit, wherein a voltage level of the compensating pulse supplied from the power source to the signal drive circuit is changed in accordance with a control signal. The control signal is preferably a polarity signal. According to this configuration, the peripheral circuit including the power source circuit and drive IC can be simplified, so that a compact and inexpensive LCD can be realized while suppressing the crosstalk properly.
A second configuration of the drive circuit for an LCD according to the present invention comprises a signal drive circuit using the above explained drive IC and a power source circuit, wherein a voltage level of the compensating pulse supplied from the power source to the signal drive circuit is changed in one horizontal scanning period. By this configuration too, the peripheral circuit including the power source circuit and drive IC can be simplified, so that a compact and inexpensive LCD can be realized while suppressing the crosstalk properly.
A third configuration of the drive circuit for an LCD according to the present invention comprises a power source circuit for generating voltage levels for a signal voltage and a compensating pulse having a predetermined waveform; and a drive IC having an input terminal for receiving the voltage levels. According to this configuration, uniform display properties can be obtained. It is preferable that the power source circuit includes at least one of a half-wave rectifier circuit and a triangle wave generator circuit. Using such a simple signal generator circuit, an LCD having uniform display properties can be provided.
A fourth configuration of the drive circuit for an LCD according to the present invention comprises a power source circuit for generating voltage levels of a scanning voltage, a signal voltage and a compensating pulse; a signal drive circuit including a drive IC having an input terminal for receiving the signal voltage, with the power source circuit including a voltage divider circuit using resistors for generating the voltage level of the compensating pulse. It is preferable that the power source circuit further includes an inverter circuit for inverting the voltage level of the compensating pulse. It is also preferable that the voltage level of the compensating pulse varies along with a drive voltage of the liquid crystal display. Thus, good display properties can be maintained without losing the condition of the crosstalk compensation when readjusting an intensity of the display or changing the bias resistor to optimize the display properties in the manufacturing process.
A fifth configuration of the drive circuit according to the present invention is for an LCD that includes a plurality of scanning electrodes and signal electrodes arranged in a matrix, and the signal electrodes are divided into upper and lower parts. This drive circuit comprises two compensating pulse control circuits for controlling the upper and lower parts independently from each other. According to this configuration, the compensation amount can be controlled in accordance with a crosstalk amount that may be different between upper and lower parts of the display depending on the display pattern. Thus the crosstalk compensation can be performed properly both in the upper and lower parts of the display, and a boundary line between the upper and lower parts of the display can be suppressed.